Nitropolycyclic aromatic hydrocarbons (nitroPAHs) are a structurally diverse group of mutagenic and carcinogenic materials occurring in association with submicron particles in polluted air. The atmospheric photochemistry of particle-bound nitroPAHs will be simulated in laboratory studies to determine their probable environmental fate. The long-term project objective is to assess the relative hazard to human health of weathered atmospheric particles and fresh particulate emissions. Specific aims include the following: (1) determination of the intrinsic photochemical reactivity of 1-, 2-, and 9-nitroanthracene in the solution phase; (2) definition of the effects of solvent hydrogen-donating capacity and triplet sensitizers on (1); (3) simulation of the atmospheric photochemistry of the nitroanthracenes by irradiating vapor-deposited materials on diesel exhaust particles, coal fly ash, and urban atmospheric particulate matter; (4) determination of the mutagenic potency of the substrates and transformation products using the Salmonella typhimurium/mammalian microsome bioassay; (5) assessment of the bioavailability of adsorbed mutagens in human fluids by measurement of their desorption in horse serum and aqueous buffers. The proposed research will test the hypothesis that nitroPAHs are photoinactivated to polycyclic quinones on atmospheric particulate surfaces as well as evaluate alternate photodegradation pathways. The subsequent bacterial mutagenesis assays and desorption studies provide a means for determining the effects of atmospheric photochemistry on potential human carcinogenicity and bioavailability of adsorbed mutagens and carcinogens in the human lung.